Conventionally, when inserting a wire harness routed in an automobile into a through-hole of a vehicle body panel, a grommet is externally fitted and attached to a wire harness and the grommet into which the wire harness is inserted is mounted in a through-hole of the vehicle body panel. Thereby, the portion of the wire harness inserted in the through-hole is protected from water and dust.
In this kind of grommet, there are many cases in which a peripheral edge of the through-hole of the vehicle body panel is fitted to an annular groove portion provided on an outer periphery of the grommet; however, as shown in FIG. 5, there are also cases in which a bolt 5 fixated on a peripheral edge of a through-hole 4 which has been bored in a vehicle body panel 3 is inserted into a bolt hole 2 provided on a grommet 1, and then the grommet 1 is adhered to the vehicle body panel 3 and is fastened and fixated by the bolt 5 and a nut (not pictured) (see Japanese Patent Laid-open Publication No. 2001-309528). Even when the grommet is attached to the vehicle body panel by bolt fastening in this way, it is possible to improve the stability of the adhered state between the grommet and the vehicle body panel, and to maintain waterproofing and debris-proofing functions of the grommet.
In this kind of grommet for a vehicle, in addition to waterproofing and debris-proofing performance, sound insulation performance which stops noise of the engine compartment and the like from leaking into a vehicle cab side through the through-hole has also been fiercely sought after. In many conventionally supplied grommets having high sound insulation ability, a portion of the grommet disposed outside a vehicle cab has a two-walled structure having interior and exterior walls, and has included a sealed space for sound insulation between the interior and exterior walls. In addition, there are also cases where a sound insulation sheet (silencer) is applied to a vehicle cab side surface, surrounding a wire harness through-hole of a vehicle body panel. Any of the sound insulation solutions for a vehicle cab interior described above is effective; however, even better vehicle cab sound insulation has been sought, and in this regard there is room for improvement of a grommet.